Field
The invention generally relates to a method for sequencing a plurality of tasks performed by a processing system and a processing system for implementing the same.
Description of the Related Art
In semiconductor manufacturing, there is often a length of time, known as queue time, during which a substrate may have to reside outside the process station or controlled environment for a period of time while waiting for that equipment to become available. During the queue time, the substrate may be exposed to ambient environmental conditions that include oxygen and water at atmospheric pressure and room temperature. As a result, the substrate subjected to oxidizing conditions in the ambient environment may accumulate native oxides or contaminants on the metal surface prior to the subsequent metallization process.
Often, there is a constraint between a deposition of a dielectric layer on a substrate and a post deposition anneal process. For example, anneal process must begin within a certain time after the deposition of the dielectric layer is complete. This type of constraint is referred to as a queue time limit. Generally, a queue time limit is a constraint between two tasks, for example, Task 1 and Task 2. Generally, Task 1 must occur before Task 2. When there is a queue time limit between the two tasks, Task 2 must also begin within a certain amount of time after Task 1 is completed. Thus, Task 2 cannot begin until after Task 1 is complete, but also must begin before the queue time expires. This relationship may be expressed as:T1>T2>T1Duration+Queue Time Limit.
Where T1 represents Task 1, T2 represents Task 2, T1Duration represents the time it takes T1 to complete, and the Queue Time Limit represents the time within which T2 must begin after the completion of T1.
Queue time constraints pose significant sequencing hurdles because once a process that starts the queue time is scheduled, that process limits the time range where the later operation can be scheduled. For example, once deposition is scheduled, the deposition process limits the time range where a subsequent related anneal process may be scheduled. After several such processes are scheduled, there are subsequent processes with limited start time ranges. There is no existing mathematical algorithm to determine if there is sufficient capacity to schedule the subsequent processes, short of iteratively scheduling them.
Thus, there is a need for a method to more effectively schedule a plurality of tasks to be performed by a processing system.